Dewan: Which teams are the most improved defensively?

From SABR member John Dewan at ACTA Sports on June 6, 2014:

The Cardinals were an exceptional team last season. They finished tied with their eventual World Series opponent Red Sox for the most wins in baseball (97). They were fifth in baseball with a 3.42 team ERA and third with a .332 on-base percentage. However, that excellence did not extend to their defense. Baseball Info Solutions estimates their fielders combined to cost the team 39 runs, which was second worst in the NL, ahead of only the Phillies.

If their start to the 2014 is any indication, the Cardinals have dramatically overcome that weakness. So far, Cardinals defenders have saved their team 40 runs. That’s a 79-run improvement over last year already and 10 runs more than the second best team, the Brewers. Using the 10 runs per win rule of thumb, that theoretically translates to a seven or eight win defensive improvement. If you prorate their Defensive Runs Saved total over a full season, the Cardinals are on pace to become the team with the biggest defensive turnaround from last season by a wide margin.